Low density cellular explosive foam



Aug. 14, 1962 H. .L STARK Low DENSITY CELLULAR ExPLosIvE FOAM 3Sheets-Sheet l Original Filed Aug. 15, 1955 mmmcomm @2 0402 .AI

mmmOOm-A 025402 INVENToR. HOWARD J. STARK A T TOYRNE Y Aug. 14, 1962 H.J. STARK 3,049,454

LOW DENSITY CELLULAR EXPLOSIVE FOAM Original Filed Aug. 15, 1955 3Sheets-Sheet 2 '.FoAMEo l l xPLoSnvraY l DETONATUR EXPTSSIVE $0 66XDETONAT R W ExPLoslvE o FIG. 6`.

WARHEAD FOAMED EXPLOSIVE 74 ENGNE HIGH EXPLOSIVE 70 FIG. Z

JNVENTOR. H0 WARD .l STARK Aug. 14, 1962 H. J. STARK LOW DENSITYCELLULAR EXPLOSIVE FOAM 3 Sheets-Sheet 3 Original Filed Aug. l5, 1955FIGB.

FIG. 9.

FOAMED EXPLOSIVE JNVENTOR. HOWARD J STARK BY E ATTORNEY 3,049,454Patented Aug. 14, 1962 ice LOW DENSITY CELLULAR EXPLOSIVE FAJW Howard J.Stark, 920 N. Lebanon St., Arlington, Va. Original application Aug. 15,1955, Ser. No. 528,566, now

Patent No. 2,768,072, dated (Pct. 23, 1956. Divided and this applicationApr. 25, 1956, Ser. No. 580,677

6 Ciaims. (Cl. 149-92) (Granted under Title 35, U.S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the pay ment of any royalties thereon or therefor.

This invention relates to low density explosives and in particular to alow density, cellular explosive foam.

This is a related application to claim the subject matter required to bedivided out of copend-ing application Serial No. 451,723, liled August23, 1954, no-W Patent No. 2,845,025 issued July 29, 1958, and entitledLow Density Cellular Explosive Foam and Products Made Therefrom, andwhich was a continuation application of then copending and now abandonedapplication Serial No. 185,900, tiled September 20, 1950, and entitledLow Density Cellular Explosive Foam. This is a divisional application ofcopending application Serial No. 528,566, filed August 15, 1955, nowPatent No. 2,768,072 issued October 23, 1956, and entitled Method ofProducing a Low Density Explosive which was a continuationinpartapplication of then copending and now abandoned application Serial No.300,367, filed June 30, 1952, and entitled Low Density CellularExplosive Foam which was a divisional application of Serial No. 185,900,supra.

The general object of the invention is to provide an explosive having acellular foam structure which, because of such foam structure, is ofrelatively low density, is buoyant with respect to water, and of greaterand more rapid shattering effect than the same weight of high densityexplosive.

It is also an object of the invention to provide an explosive having acellular foam structure which is set and rigid and which is relativelystrong and tough.

It is a further object of the invention to provide an explosive having acellular foam structure which may be cast or molded into a particularshape prior to the setting or assumption of rigidity.

Other objectives will be apparent from the following description andfrom the drawings, hereto attached, which are illustrative of the methodof making the cellular explosive and of the preferred embodiments of theinvention.

In these drawings:

FIG. 1 is a flow chart of the dynamic air-set method of this invention;

FIG. 2 is a ow chart of the chemical blowing method of this invention;

FIG. 3 is a diagrammatic transverse section through a conventionalfloating mine;

FIG. 4 is a diagrammatic transverse section through a oating mine of thetype illustrated by FIG. 3 but containing a relatively large quantity ofthe foamed explosive of this invention cast in situ;

FIG. 5 is a diagrammatic sectional-elevational View of a floating minein which the shell is comprised of the molded foamed explosive of thisinvention encased in light weight metal or impregnated fabric and showsthe increased high explosive charge possible with this type ofconstruction;

FIG. 6 is a diagrammatic longitudinal section through a floating, harbormine showing the combination in the explosive charge of the conventionalhigh density explosive with the foamed explosive of this invention;

FIG. 7 is a diagrammatic longitudinal sectional-elevational view of atorpedo carrying a charge of high density explosive and foamed explosiveof this invention; and

FIGS. 8 and 9 are a diagrammatic longitudinal sectional-elevational Viewand a transverse sectional view taken on line 9 9 of FIG. 8,respectively, of a radio controlled homing vessel showing the foamedexplosive of this invention cast and molded within the structure of thedouble walled hull.

Heretofore, it has been the practice, in the manufacture of explosive,to produce them with a relatively high density in order to have a greatexplosive effect in a given volume. Now a requirement has arisen inwhich it is desirable to have an explosive which is buoyant and whichmay have a greater explosive effect which may be additive to that of theconventional high density explosive. This requirement is present notonly in oating mine structures, but also in the guided surface (theSocalled homing) vessels.

This inventor has met this requirement by providing a foam typeexplosive which resembles in physical appearance and characteristicscellular polystyrene or cellular acetate. It is relatively strongandtough and the density thereof can be varied by formulation Within therange of from about 5 to about 50 pounds per cubic foot.

The cells of the foamed and set structure of the explosive aresubstantially non-communicating and referred to as closed-cells incontradistiction to spongy open-cells. Therefore, a molded plate of thismaterial is relatively impervious to gas and water. In comparison withbalsa wood, which has a buoyancy of about twenty pounds per cubic footafter twenty-four hours immersion under a ten foot head of water, thiscellular explosive has a buoyancy of from about 20 to about 50 poundsper culbic foot under similar conditions.

The following explosives, as well as others, can be prepared in foam orcellular form: (l) Trinitrotoluene (2) Nitrocellulose (tri, hexa anddodeca nitrocellulose) (3) Pentaerythritol (4) RDX (cyclotriemethylenetrinitramine) The foamed explosive consists essentially ofany one of the above explosives bonded by a foaming plastic.

A foaming plastic is a plastic which will be of solid cellular structurewhen it is allowed to set after being foamed either by chemically ormechanically blowing gas or air through it while in the liquid stage aswill appear in the example set forth below.

This inventor has found that polyesters of ethylene glycol-maleicanhydride intermixed with monomeric styrene is ideally suited as a resinin the carrying out of this invention. This resin is shown and describedalong with other resins which also are suitable in Carleton Ellis Patent2,255,313, which is incorporated by reference and forms a part of thisspecification. Of course a ller as used in the examples of Ellis isunnecessary and not used although such use would still fall Within thescope of what is considered to be the present invention.

An example of one of these resins is that produced by heating 500 partsof maleic anhydride and 541 parts diethylene glycol in an oil bath at220-225" C. for 7 hours while bubbling nitrogen gas therethrough toprovide an inert atmosphere. The diethylene glycol maleate formed is alight-colored viscous liquid of acid number 7.1. Eighty-tive parts ofthis liquid are mixed with 5 parts monomeric styrene in a glasscontainer with a mechanically driven stirrer. The resultant liquid is asatisfactory stock solution and has 3% (by weight) benzol peroxide(curing agent) and 31/2% (by weight) cobalt naphthanate (accelerator)added to it just prior to its use.

' priate curing agent.

to as settingk agents. f

` blowingk method. These These bonding thermosetting polyester resinsare well known in. the field of resin chemistry and their specificcompositions form no part of this invention. The requirernents thereofare that they be compatible with solutions ofthe explosives, that theygel at room tern- 1 sivel sui'cient to prevent the escape of airtherefrom and yet be suliiciently fluid forefcient molding aud casting.The rateA of setting of these resins is controlled by the additionthereto of a relatively' small proportionl (from about 2% to' about 4%by weight) of an approinclude: benzol peroxide, ditertiarybutylperoxide, cumenehydro peroxide, methylisobutyl ketone peroxide,

'and dibenzaldeperoxide. yThe choice ofthe 'particular curing agent useddependsupony its compatibility with the solution of the1 resin'and theexplosive andthe rate, of curing desired. Also an accelerator, suchascobalt naphthanate may be `added in a proportional amountl of fromabout 2%' to about 5% by weight to give additional 'control' on the rateof geliing and setting of the resin.

These curing agents and accelerators are herein referred Commerciallyavailable resins which have been foundk to be suitable as a bond for thefoamed explosives of this l invention are yMR-28C' and 29C by MarcoChemicals,

Inc., Selectron 5003 and 5016 produced and-marketed l 'by the PittsburghPlate Glass Company, Laminac 4128, 4129 and 41116 produced and marketedby the American Such agents have been found to Cyanamid Company, andParaplex P-43 by Rohm andy f Haas Company.

Two methods of the preparation of foamed explosive are preferred by thisinventor. 'Ihese are (l) the soealled dynamic air-set method, and (2)the chemical methods differ from each other mainly in the methodofintroduction of the resinous solution of the explosive.. In the dynamicair-set method (reference being had to FIG. lof the drawings), asolution of the explosive'in styrene, ether, acetone, or a mixture ofsome of these or other solvents is made as indicated at 110. Only asmuch explosive may be dissolved as Will go into the solution with orwithout the -application of a moderate heat, and with staying below thedecomposition temperature of the cxplosive, A solution of a foamingplastic such as polyester type resin, a curing agent or catalyst and anaccelerator is prepared as shown at 12 in the proportionate amountsabove indicated. From about to about 30% by volume of the liquid resinsolution is mixed with the solution of the explosive as shown at 14.

As an example, the diethylene glycol maleate with monomeric styrene ismixed with benzol peroxide and cobalt naphthanate as specifically setforth above. About 20% by volume of this solution is mixed with asaturated solution of TNT dissolved in styrene.

The curing agent and accelerator will cause the resin to gel in about 15minutes and to set permanently in about one hour. The mixture ofsolutions of the explosive and resin is stirred for about 5 minutes asindicated at 15 and allowed to rest for about 5 minutes. Compressed airfrom a source (not shown) is introduced into blowing chamber 18 andthence through yforaminous member 20 which may be a glass frit or metalscreen of a mesh in the range of from 75 to 300 and through the mixtureat 14 for about 3 minutes which will foam the said mixture. The foamedmixture is then poured into molds or other containers within theremaining 2 minutes of the 15 at which time the foamed explosive gels orsets up and in one hour becomes a hard cellular mass. By a propercontrol of the viscosity of the mixture, above referred to, air bubblesdo not appreciably escape therefrom after the completion of the blow orduring the period that the mixture is in the mold prior air or gas intof addition of a curing agent and an accelerator to a foaming plastic inthe proportionate amounts above indicated and as shown at 26. Thefoaming plastic may be a poly-l ester type resin as above described orother foaming plastics set lforth below. In either casethey are adjustedto gel in about fifteen minutes and to set. in aboutl l one hour as inthe process'a-bove described. The solutions of. the lexplosive and theresin are conducted into mixing chamber Z8, the solution of the resinbeing added. in the proportion by volume of from 10% to 30%. In thischamber there is added to the mixture from 10% to 30% by volume of 1achemical blowing agent such as diazoaminobenzene or toluenediisocyanate. The mixture is stirred, as indicated at 30 for from tiveto ten .minutes and is then poured or cast into molds as indicated at32. The molds are thenl heated as indicated at 33 toa temperature ofabout 120 C. but not above decomposition temperature of the explosiveatk which temperature the blowing agent evolves a relatively largervolume yof gas which causes the massto expand forming a cellularstructure. 1 1 1 1 The range inA composition, .ony a percentage weight 1f basisy at various temperaturesof for-mation, of the foarned explosivesof this invention is givenk inthe following table:

PRei-eent Plrceut Ircent ange ange ange C. Temp. Solvent in Explosive inin Comp. Comp Comp.

ofRcsin 20T acetone 10-30 10-30 10-30 10-30 10-30 10-30 10-30 5 10 10 25eyclohexal0 none. 60 acetone 15 cyelohexa- 15 none. do 78 HBX-l & 2 1210 acetone 67 HBX-l &2 18 15 cyclohexa- 60 HBX-l dz 2..- 25 15 none.

Other examples using different foaming plastics are set forth below andit will be understood by a chemist familiar with the art that suchfoaming plastics are capable of use with the dynamic air-set method aswell as the chemical blowing method.

A chemically blown foamed explosive can be prepared by using toluenediisocyanate and alkyd resins to produce a composition referred to inthe art as polyurethane foam resins. Carbon dioxide is liberated in thereaction to cause the plastic to foam and thus, in effect, theingredients act as their own blowing agents.

For purposes of this invention an alkyd resin having followingcomposition is prepared:

7.6 parts by weight glycerol 5.0 parts by Weight adipic acid 1.0 part byweight phthalic anhydride These ingredients are refluxed in a glasslined container in an atmosphere of carbon dioxide and at a temperatureof about 165 C. until an acid number of about 55 and hydroxyl number ofabout 415 are reached. The alkyd resin thus formed is then cooled toroom temperature for further use as described below.

Ratios of explosive to resin by weight range from 10% resin to explosiveto 50% resin and 50% explosive.

Optimum results are obtained where to 30% of resin is used with 90 to70% of explosive. The following composition is prepared in the followingmanner to produce a polyurethane explosive foam:

(A) 150 parts by weight of alkyd resin as prepared above.

(B) 1350 parts by weight of TNT contained in warm acetone (about 30 C.).

(C) 140 parts by weight 2-4 M-toluene diisocyanate.

(D) 58 parts by weight-of water.

Ingredients (A) and (B) are first mixed in a mechani# cal mixer such asa Hobart of suitable capacity. Then ingredient (C) is mixed therewithfollowed by ingredient (D) which is mixed therewith or stirred for about20 minutes.

This mixture is then poured into a suitable metal mold calculated toproduce the desired density which in this case is about l0 pounds percubic foot. The closed mold containing the mixture is then placed in ahot air oven at about 73 C. for about one hour after which the mold isremoved from the hot air oven and cooled to room temperature and theexplosive TNT foam is removed therefrom.

Another example of a manner of practicing the invention, which in thiscase utilizes a polyvinyl chloride resin with a copolymer of vinylchloride and vinyl acetate, follows:

About 100 parts of a polymerized material consisting of about 85% byweight of polyvinyl chloride and about by Weight of copolymers of vinylchloride and vinyl acetate are mixed in a Hobart mixer with about 80parts of tricresyl-phosphate (plasticizer) until the polymer isthoroughly dispersed. About 25 parts of P.P'oxybis benzene sulfonylhydrazide (chemical blowing agent) is then added and mixed thoroughly.(Diazoaminiobenzene or 40% dinitroso pentamethylenetriamine may also beused as chemical blowing agents.) About 3 parts of lead stearate(stabilizer) is also added and mixed thoroughly.

About 80 parts by weight of TNT in a fine state of division such as willpass through a Standard Sieve No. 50 or 100 (as delined by the AmericanSociety for Testing Materials Standards) is then added to the abovecomposition and the mixture worked to a uniform consistency with a stiffblade mechanical mixer. About 10% by weight of the combined ingredientsof acetone is then added slowly and the mass mixed to uniformconsistency.

A suitable charge or volume of this product is placed in a steel mold ofdesired shape. Such an example would be a mold 6 x 6" x 1/2 of heavysteel wall construction as established in the art or industry forprocessing these products. The mold cavity is completely illed, and thecharged mold placed in between press platens at a temperature of about160 C. The press is then closed and about 5000 p.s.i. pressure appliedto the mold and held for about minutes at this temperature. After thistime the pressure is reduced to atmospheric and the mold removed fromthe press. rThe mold is opened and the molded piece is removed. It isthen placed in a hot air oven or chamber at about 120 C. for about 60minutes when the piece will then grow or expand to about double itsvolume producing a density between 4 and 7 pounds per cubic foot. Thedensity can be considerably changed by varying the charge into the moldand the weight of explosive incorporated into the mold.

An epoxy resin can be used in carrying out the invention in a mannersuch as shown by the speciiic example below.

About 110 parts of a diphenol such as bisphenol A is dissolved in 80parts thereof of a 20% Water solution of sodium hydroxide. About 188parts of epichlorohydrin is slowly added to the mixture at about 75 C.over approximately a 30 minute period. The resulting resin melts atabout 65 C.

Explosive foam mixture is prepared using the following ingredients:

Parts Epoxy resin as above 98.0 Ammonium bicarbonate (blowing agent)10.0 Diglycol laurate S (wetting agent) 3.5 Piperidine (curing agent)2.0

TNT 400.0

Epoxy resin as above is heated to the liquid stage at about 75 C. Theammonium bicarbonate previously dispersed in diglycol laurate S is thenadded and stirred thoroughly. The TNT is then added and stirred,followed by the piperidine which is then added and mixed for about 5minutes. The liquid phase life at this stage is limited to about 30minutes; otherwise, polymerization or solidification sets in. Themixture is then transferred to a heated metal mold or box held at about75 C. for about 2 hours when the explosive foam is made. The explosivecompletely fills the container. Of course the explosive foam mixturesmay also be made from nitrocellulose, pentaerythritol, and cyclotrimethylenetrinitramine. The density of the explosive foam iscontrolled by varying the percentage of explosive going into thecomposition and the weight of mix going into the heated mold cavity orbox as described above.

This particular explosive foam composition may also be cured using otheramine reagents such as diamines, triamines or quaternary amines such as,diethylenetriamine and triethylenetetramine. Commercial resins such asShell Chemical Company Epon resins such as Epon 834, Epon 864, and Epon1001 and mixtures of these various resins may also be used. Cure orhardening is accomplished by using any one of the amines stated above.

Referring further to the drawings, in FIG. 3 a conventional iloatingmine is shown diagrammatically and generally at 40. The mine comprises ametallic case 4Z, contact elements 44 which are in electric circuits 46with the detonating or exploding device 48. This exploding devicedetonates the charge of high explosive 50 when any one of the elements44 is actuated by contact with an object in the water. The interiorvolume of this type of mine is comprised of about 50% air space as shownat 52.

In FIG. 4 the air space of the mine shown in FIG. 3 is filled with thefoamed explosive of this invention as shown at 54 which has been curedand set in place. This foamed or cellular explosive not only gives anadditive eect to the brisance of the high explosive, but in the event ofleakage through metallic shell 42 due to erosion or corrosion thereof,the buoyancy of the mine will be maintained substantially as thatexisting when the mine is in leakproof condition.

FIG. 5 is illustrative of an embodiment of this invention in which theshell of the mine is comprised of molded cellular explosive 56 coveredon the exterior and interior faces with a relatively thin layer of metalor impregnated fabric 58. The increased buoyancy of this type ofconstruction over the conventional, heavy metallic case mine is readilyapparent. in fact, the buoyancy is so much greater that substantiallythe entire interior space of the mine may be lled with high densityexplosive thereby producing a mine of greatly increased shatteringeffect when also considered in the light of the additive explosiveelfect of the cellular explosive comprising the shell.

FIG. 6 is a sectional illustration of a floating harbor mine showing thearrangement of a metallic casing 60, a high density explosive charge 62,detonating or exploder device 64, actuating contact element 66 andfoamed explosive of this invention 68 surrounding the high explosivecharge and exploder device and filling the air space normally presentwithin the casing of this type of mine. In the event of leakage of waterthrough the casing due to corrosion thereof or otherwise, the foamedexplosive prevents loss of buoyancy and the normally resultant loss ofthe mine.

FIG. 7 is a sectional-elevational view of a torpedo shown generally at70 in which the foamed explosive 72 of this invention fills the normallypresent air-space within the shell 74. The legends in this figure arebelieved to be self-explanatory. In this embodiment of the invention,the overall buoyancy of the torpedo is less than that of the torpedohaving the conventional air space. But the total shattering effect ofthe explosion is much increased by this additional quantity of foamedhigh explosive. In charging this cellular explosive into this air spacein the torpedo, the foamed explosive is poured into this spaceimmediately prior to the gelling thereof. The space is completely filledand upon the curing and setting of the resin component the cellularexplosive becomes rigid and reinforces the sidewalls of the shell.

FIGS. 8 and 9 show the application of the foamed high explosive of thisinvention to the structure of an electronically controlled homing vesselin sectional-elevational views. Here the double walled hull 90 is shownprovided with radio control 92 for motor drive mechanism 94. Highdensity high explosive 96 substantially fills the interior of hull 90surrounding the exploder device 98. The detonating contact element isshown at 99. T he space within the double wall structure of the hull isfilled with the foamed high explosive of this invention as shown at 100.As in the case of the torpedo above-described, the foamed explosive ispoured into this hull wall spaced irnmediately prior to the gelling andafter setting the foamed cellular explosive mechanically reinforces thestructure. The advantage of this type of construction of these homingvessels is that the shattering effect of the explosion is greatlyincreased and that in the event of leakage through the outer wall of thehull due to corrosion or to any other cause the buoyancy of the vesselis maintained.

It should be understood, of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that it isintended to cover all changes and modifications of the examples hereinchosen for the purposes of the disclosure, which do not constitutedepartures from the spirit and scope of the invention as set forth inthe appended claims.

I claim:

1. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and impervious tothe passage of fluid, said foam being a homogeneous mixture of about 90percent to about 70 percent by weight of an explosive from the groupconsisting of trinitrotoluene, nitrocellulose, pentaerythritol, andcyclo trimethylenetrinitramine and a binder of about 10 percent to about30 percent by weight of a thermosetting polyester resin.

2. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and are imperviousto the passage of uid, said foam being a homogeneous mixture of about 8Spercent to about 67 percent by weight of trinitrotoluene and from about12 percent to about 33 percent by weight of a thermosetting bondingpolyester resin.

3. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and are imperviousto the passage of fluid, said foam being a homogeneous mixture of about85 percent to about percent by weight of nitrocellulose and from about15 percent to about 40 percent by weight of a thermosetting bondingpolyester resin.

4. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and are imperviousto the passage of fluid, said foam being a homogeneous mixture of about85 per cent to -about 75 percent by weight of pentaerythritol and fromabout 15 percent to about 2.5 percent by weight of a thermosettingbonding polyester resin.

5. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and are imperviousto the passage of fluid, said foam being a homogeneous mixture of aboutpercent to about 55 percent by weight of cyclo trimethylenetrinitramineand from about 35 percent to about 45 percent by weight of athermosetting bonding polyester resin.

6. An explosive whose density is less than that of water which comprisesa foam wherein substantially all the cells are closed and impervious tothe passage of uid said foam being a homogeneous mixture of about 90percent to about percent by weight of trinitrotoluene and from about 10percent to 30 percent of an alkyd resin.

References Cited in the file of this patent UNITED STATES PATENTS2,062,011 Norman Nov. 24, 1936 2,165,263 Holm July 11, 1939 2,171,379Wahl Aug. 29, 1939 2,334,149 Ripper Nov. 9, 1943 2,349,048 Mackey May16, 1944 FOREIGN PATENTS 674,447 Great Britain June 25, 1952

1. AN EXPLOSIVE WHOSE DENSITY IS LESS THAN THAT OF WATER WHICH COMPRISESA FOAM WHEREIN SUBSTANTIALLY ALL THE CELLS ARE CLOSED AND IMPERVIOUS TOTHE PASSING OF FLUID, SAID FOAM BEING A HOMOGENEOUS MIXTURE OF ABOUT 90PERCENT TO ABOUT 70 PERCENT BY WEIGHT OF AN EXPLOSIVE FROM THE GROUPCONSISTING OF TRINITROTOLUENE, NITROCELLULOSE, PENTAERYTHRITOL, ANDCYCLO TRIMETHYLENETRINITRAMINE AND A BINDER OF ABOUT 10 PERCENT TO ABOUT30 PERCENT BY WEIGHT OF A THERMOSETTING POLYESTER RESIN.